We spent a night here to split the route between PP and Siem Reap and were agreably surprised by the hotel and the city.
Location is perfect (right where the bus dropped us, and right next to the market and the river). Our budget room cost 5 usd and had no window. Very small but adequate furniture and very clean sheets and bathroom. Bug servings at reasonable prices in the popular restaurant downstairs.
Only problem was that we could hear the music from the karaoke in the evening. Do prepare earplugs! Still great value for money and this is the place we'll stay at next time we are in town.
Not related, but for those breaking the route like us you might want to know that the cheapest way to reach Kampong Thom from PP by bus is with a ticket to Preah Vihear from GST company (psar thmei area just behind phnom penh sorya). It costs $5/person. Kompong Thom to Siem Reap costs $4 (right in front of Arunras hotel) by bus. Alternatively just walk away from the ticket vendors and stop any local minibus heading East. You should be able to negotiate $3/person directly with the driver.